Basement waterproofing for local leisure centre development


Client: GTCI Ltd

Products Used: MS500 Cavity Drain Membrane, MS20 Floor Membrane, Vandex BB75E, Perimeter Drainage Channel, Pumping Stations

Constructed almost 50 years ago, and built from a traditional dark red high-density brick, the two storey building in question had a very large below ground void that had become increasingly affected over the years by water ingress, from the changing water table. When this building was originally constructed it was not uncommon for them to include a large belowground basement however little or no thought was given to waterproofing at this period in time.

The basement rooms were not in use but had previously been a health suite with plant and storage rooms. The walls had been rendered with dense sand and cement and the floors overlaid with concrete. High moisture levels were recorded in several locations with high levels of salt contamination to the skim plaster. Timberwise were tasked to design and install a basement waterproofing system, due to the property being converted into a leisure centre with accompanying swimming pool.

Hard rendered walls were, and still are, commonly known as tanking, and up until a few years ago, this was really the only effective way to install any form of internal barrier that would keep water out. However, such systems are prone to cracking given the slightest movement of the building/substrate and as a consequence. The most minute hairline crack within the hard render coating would effectively compromise the installation allowing water in and once the case it would spread rapidly thus effectively making the internal finishing system completely ineffective.

The water table can vary, and as a consequence, the degree of water pressure can fluctuate, and at times the head of pressure could be more than any cementitious system could realistically resist. Therefore, by using a membrane system you actually equalise the pressure and relieve the building of unnecessary stress.

The Waterproofing Design Methodology

Based on a poor previous experience the client did not want any form of internal cementitious render waterproofing, however, they were aware of the existence of cavity drain membrane systems. The client was therefore very receptive to Timberwise’s proposal of a complete wall and floor cavity drain membrane solution alongside a perimeter drainage channel, and four subfloor sump and pump chambers.

One of the often overlooked benefits of an internal cavity drain membrane is that by definition it has a degree of flexibility and tolerance built within the manufacture of the product, thus allowing it to withstand movement which can occur naturally in such buildings without actually compromising the installation. The other feature and benefit of membrane installations are that they are naturally designed to allow external water to enter a property thereby equalising water pressure, and not making the space vulnerable to a build-up of high water pressure. Previously this would have held back by a hard render system which could at any time under such pressure have given way and caused substantial flooding/damage.

Furthermore, it is very difficult to affix battens to a hard rendered wall for the subsequent installation of plasterboard and other similar finishing systems. Before work could commence, a full specification of preparation works was carried out for the builder by Timberwise, to seamlessly install the necessary waterproofing system. The lower basement and pool area was waterproofed using a special cavity drainage membrane and special plugs to allow it to be finished either by a freestanding plasterboard system or with a mesh block wall built in front.

Generally, once such a membrane installation has been completed it is maintenance free and can, therefore, be hidden from sight in a variety of ways. The most common way is to fix plasterboard direct to the mesh membrane surface, however, if wished you can also build an internal stud framework or install a block partition wall depending upon what the intended use of the room is to be for.

Irrespective of the internal finish, as detailed above the one important criteria is that the membrane must not in any way be punctured by any internal fixtures and fittings, even including the hanging of pictures on a traditional picture hook. Clearly, if a brick wall was constructed in front of the membrane installation it is unlikely that any form of puncturing of the membrane is likely to be the case in any final fit-out works, however if the chosen finish is to be pure plasterboard dot and dabbed to the mesh membrane surface then one has to be very careful and mindful of any internal fixings

 This new leisure centre will serve all local residents. We’re proud to be part of the waterproofing design and installation team to support healthy lifestyles and compliment the growth of the area for years to come 

Keith Defoe, Waterproofing Design Specialist CSSW

In most cases where a complete membrane system is to be installed, both on the walls and the floor, together with subfloor perimeter drainage channels and a sump and pump system, then such installations would be designed to comply with BS8102: 2009, which is the British Standard required in all such installations.

The design work has to be undertaken by a surveyor with the minimum qualification of a CSSW qualified surveyor, and one should never take for granted or underestimate the potential issues that can be caused by a non-compliant specification/installation. Furthermore, due to the size of the system and evidence of natural deposits within the underlying water table, Timberwise incorporated regular inspection ports within the channel to allow easy access for servicing.


Once the system had been installed and electrically commissioned Timberwise undertook a flood test to demonstrate to the client first hand, that water flowed away freely and that all of the sumps and pumps operated as planned, pumping water to the designated outlets and into the accompanying drainage. The customer, via their own contractor, was able to finish the internal installation by way of dry lining and decorating, thus creating a dry warm and habitable belowground environment.

Contact Our Waterproofing Specialists

You can trust Timberwise to provide you with the right waterproofing solution to damp problems in your building. Don’t hesitate to contact Timberwise by calling on 0800 288 8660 or you can request a survey. A survey through Timberwise will be able to identify the extent of the problem and determine the right waterproofing solution for you and your property.